The present disclosure relates to an image-forming apparatus comprising a load and a fixing unit for fixing an image.
A fixing unit including a heater is provided to an image-forming apparatus (multifunction peripheral, printer, copier, facsimile apparatus, or the like) of an electrophotography format, in order to heat a toner image. The heater warms a fixing member (for example, a roller or belt) for coming into contact with paper to perform fixing. A shorter period of time for warming the fixing member correlates to less of a wait time for the user from when a main power source is turned on, when a return from a power-saving mode takes place, or the like until the start of printing. In view whereof, there is known an image-forming apparatus to which the supply of electric power from a portion for storing electric power is enabled, in addition to a commercial power source, in order to ensure that electric power will be inputted to the heater.
More specifically, there is known an image formation which is provided with fixing means for fixing a toner image onto a transfer material, the fixing means enclosing a heat generator for using electric power supplied from a commercial power source to generate heat, and which has: a power-storing means capable of supplying electric power to a load other than the heat generator; a temperature-detecting means for detecting the temperature of the fixing means; and a controlling means for controlling the electric power being supplied to the fixing means from the commercial power source, in accordance with a temperature detection result. This configuration is an attempt to make effective use of the upper-limit electrical current (electric power) of the commercial power source to achieve on-demand fixing in which the temperature rises promptly.
Firstly, due to factors such as the acceptable electrical current of an outlet, there are limitations (a limiting value, an upper limit value) to the magnitude of electrical current that can flow to the image-forming apparatus or the outlet in the use of the commercial power source. As such, when the image-forming apparatus is being used, it is necessary to prevent the electrical current flowing to the image-forming apparatus (the sum of the electrical current flowing to the load and the electrical current flowing to the fixing unit=the total electrical current) from exceeding a limiting value. Though the limiting values vary from country to country, the maximum value of electrical current that can flow to one outlet in the case of a household, business office, or the like is often up to about 15 A to 20 A in the U.S.A. and Japan. Thus, in some cases, there has been a desire to keep the total electrical current of the image-forming apparatus at a target value (for example, the limiting value) serving as a certain limit.
In addition to the heater of the fixing unit, however, the image-forming apparatus is also provided with other electrical loads (hereinafter, simply referred to as a “load”) such as a CPU for control, a memory for storing data, and a motor for rotating a variety of rotating bodies for conveying paper and the like. Often, for example, these loads are driven by direct current, and the magnitude of the drive voltage is established in advance. In view whereof, one or a plurality of power source circuit section(s) (for example, a converter) for carrying out rectification and/or stepping up/down the voltage to generate the voltage needed is/are ordinarily provided to the image-forming apparatus, in order for electric power to be supplied to each of the loads at an appropriate voltage.
In order to rapidly warm the fixing member without giving rise to a defect in the operation of the image-forming apparatus, preferably, electric power is inputted (an electrical current is made to flow) to the heater so that the total electrical current of the image-forming apparatus reaches a target value (limiting value) while adequate electric power is also being supplied to the loads, such as to the CPU. In other words, the output of the heater can be made to be a maximum output, within an acceptable range, when an electrical current obtained by subtracting the electrical current to the loads such as to the CPU from the target value of the total electrical current of the image-forming apparatus is made to flow to the heater.
In the image-forming apparatus, sometimes, alternating-current electric power based on the commercial power source is supplied to the heater while a phase control is being carried out. For example, within one period of the alternating-current voltage (a sine wave) of the commercial power source, a phase at which the heater is energized is sometimes altered to control the electrical current flowing (the electric power being inputted) to the heater of the fixing unit. In the phase control of such description, when the electrical current is increased, the phase difference between the alternating-current voltage waveform and the point in time where electric power distribution to the heater is turned on is reduced in size (the distribution of electric power to the heater is turned out at a timing that is earlier from the zero-crossing). When the electrical current is reduced, however, the phase difference between the alternating-current voltage waveform and the point in time where electric power distribution to the heater is turned on is increased in size (the timing for turning electric power distribution to the heater on after the zero-crossing is delayed). Also, generally, the power factor in the fixing unit becomes larger as the phase difference becomes smaller (for example, the power factor is 1 when the phase difference is zero). However, the power factor in the fixing unit becomes poorer as the phase difference becomes larger.
The total electrical current of the image-forming apparatus is also influenced by the result of combining the power factor of the power source circuit section (a power factor of, for example, about 0.6) and the power factor of the fixing unit. The electric power consumed by the heater mounted onto the fixing unit of the image-feinting apparatus is 1,000 watts or more. The electric power consumed by the heater is thus ordinarily greater than the electric power consumed by the load. For this reason, the total electrical current of the image-forming apparatus is dramatically influenced by changes in the power factor of the fixing unit. The power factor of the power source circuit section, too, changes sometimes depending on the output state (the magnitude of output).
For this reason, the amount of change in the total electrical current when the phase of electric power distribution to the heater is altered in an amount of the same magnitude varies depending on the state of the fixing unit prior to the change, and the like (the magnitude of the power factor of the fixing unit prior to the change, the magnitude of the power factor of the power source circuit section, and the like). In other words, the ratio of the amount of change in the total electrical current of the image-forming apparatus relative to the amount of change in the phase is not constant, and depends on the state of the image-forming apparatus.
Herein, conventionally, the total electrical current flowing to the image-forming apparatus after the phase has been altered is sometimes measured and a control for correcting the phase (feedback control) is carried out, from the standpoint of keeping the total electrical current of the image-forming apparatus at the limiting value (target value). However, the feedback control has conventionally been carried out without giving consideration to the change in the power factor of the fixing unit associated with the change in phase. In some cases, though, the amount of change in the total electrical current misses the intended amount of change even when the phase is altered, due to the influence of the change in the power factor of the fixing unit. For this reason, processing for altering the phase (phase correction processing) is repeated many times until the total electrical current of the image-forming apparatus matches the target value, and a problem emerges in that in some cases time is needed until the total electrical current can be matched to the target value. Further, because the amount of change in the total electrical value misses the intended amount of change, the target value is sometimes deliberately set to a value considerably lower than the limiting value, in order to endow a margin so as not to exceed the limiting value.
In the above-described image-forming apparatus known in the art, an attempt is made to use the power-storing means to ensure the electric power being inputted to the heater. Consideration is not given, however, to the change in the power factor of the fixing unit in the image-forming apparatus known in the art. As such, the problem where time is needed until the total electrical current of the image-forming apparatus can be matched to the target value cannot be resolved. Moreover, the total electrical current of the image-forming apparatus could exceed the limiting value in the above-described image-forming apparatus known in the art.